This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A296841 #5 Dec 21 2017 16:03:04
%S A296841 0,1,1,-12,-193,-2365,-18552,500689,48649969,2981261772,169237306055,
%T A296841 9187565146331,427287357700176,6011297159973313,-2887128048794477663,
%U A296841 -711942625068679870620,-132369975517302093882097,-22968753773651295426439021
%N A296841 Expansion of e.g.f. sin(x*tan(x/2)) (even powers only).
%F A296841 a(n) = (2*n)! * [x^(2*n)] sin(x*tan(x/2)).
%e A296841 sin(x*tan(x/2)) = x^2/2! + x^4/4! - 12*x^6/6! - 193*x^8/8! - 2365*x^10/10! - 18552*x^12/12! + ...
%t A296841 nmax = 17; Table[(CoefficientList[Series[Sin[x Tan[x/2]], {x, 0, 2 nmax}], x] Range[0, 2 nmax]!)[[n]], {n, 1, 2 nmax + 1, 2}]
%Y A296841 Cf. A001469, A003706, A009515, A110501, A296839, A296842.
%K A296841 sign
%O A296841 0,4
%A A296841 _Ilya Gutkovskiy_, Dec 21 2017